Project 1: Recombinant viruses have been generated both in vitro and in vivo from parental viruses possessing different oncogenic potential. These have been characterized immunologically in an effort to map the contributions of each parental virus. In an effort to more precisely map the viral genome, we have applied the oligonucleotide fingerprinting technique to the characterization of the recombinant viruses generated. Project 2: Although the presence of immunologically different endogenous type-C viruses in various inbred strains is well established, the way they have evolved is still unknown. Therefore, we studied the distribution of different classes of inducible viruses of inbred mouse strains from diverse geographical areas. Endpoint cloned viruses have been characterized by host range and are now being analyzed immunologically to determine their relatedness to each other as well as known endogenous viruses.